1. Field of the Invention
The present invention relates generally to an aligning station such as in a package producing machine and, more particularly, to an assembly for positioning sheet like workpieces using guides.
2. Description of the Related Art
During the production of packages from, for instance, corrugated board, sheets of corrugated board are taken from a pile and carried individually into subsequent processing stations for cutting and/or shaping, for example.
Transportation of the various successive sheets from the pile to the processing station is achieved by pushing the sheet by means of two movable guides which act as stops for the rear, or trailing, edge of the sheets, these rear guides being fitted onto an endless toothed belt. However, due to the difficulty of centering sheet pile along a lengthwise central axis of the machine, the sheets, while moving from the pile to the processing station, travel through a so-called aligning or lateral guiding station. The aligning station performs a crosswise positioning, in other words perpendicular to the direction of travel, of the various successive sheets so that the sheets are in a desired position relative to the tools of the subsequent processing station. To achieve this perpendicular positioning, the aligning station includes a reference or guiding ruler on one lateral side along which the corresponding side edge of the moving sheet is to be guided. The guiding ruler includes a guiding surface parallel to the motion of the sheet, in other words parallel to the lengthwise axis of the machine, and can be positioned crosswise. The crosswise shift of the sheet, until it touches the guiding ruler is generally obtained by means of so-called oblique rollers which are in contact with the upper side of the sheet and running either freely or are power driven with a peripheral rotary speed which includes a crosswise motion component.
Up to now, every rear guide that contacts the sheet edge has a smooth contact surface perpendicular to the direction of sheet motion. Experience has shown that when the guide driven by the belt is in contact with the cardboard, friction occurs at the contact points, which results in the following drawbacks:
A slight crosswise shift of the belt occurs during lateral shifting of the sheet so that one lateral edge of the belt rubs rather strongly against a corresponding lateral guiding device, resulting in friction which quickly wears out the belt and necessitating its change, particularly at high belt running speeds of, for example, 300 m per minute. PA0 Sheet displacement occurs due to the fact that the crosswise shifting of the sheet may be of a distance of up to 15 mm, so that the combined action of the friction forces acting on the rear guide and on the oblique rollers results in a type of swivel action which obviously would be harmful to subsequent operations since it obstructs proper lateral guidance